Shelf



FIG. 1 is a reduced perspective view of a shelf showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a side elevational view taken from the right of FIG. 3, theside opposite being a mirror image thereof;

FIG. 5 is a bottom plan view thereof.

The ornamental design for a shelf, as shown and described.